The acquisition and testing of bodily fluids is useful for many purposes, and continues to grow in importance for use in medical diagnosis and treatment, and in other diverse applications. In the medical field, it is desirable for individuals to perform tests routinely, quickly and reproducibly outside of a laboratory setting, with rapid results and a readout of the resulting test information. Testing can be performed on various bodily fluids, and for certain applications is particularly related to the testing of blood and/or interstitial fluid. Such fluids can be tested for a variety of characteristics of the fluid, or analyses contained in the fluid, in order to identify a medical condition, determine therapeutic responses, assess the progress of treatment, and the like.
The testing of bodily fluids basically involves the steps of obtaining the fluid sample, transferring the sample to a test device, conducting a test on the fluid sample, and displaying the results. These steps have been performed by a plurality of separate instruments or devices.
A common technique for collecting a bodily fluid sample is to form an incision in the skin to bring the fluid to the skin surface. A lancet, knife or other cutting instrument is used to form the incision in the skin. The resulting blood or interstitial fluid specimen is then collected in a small tube or other container, or is placed directly in contact with a test strip. The fingertip is frequently used as the fluid source because it is highly vascularized and therefore produces a good quantity of bodily fluid. However, the fingertip also has a large concentration of nerve endings, and lancing the fingertip can be painful. Alternate sampling sites, such as the palm of the hand, forearm, earlobe and the like, may be useful for sampling, and are less painful. However, they also produce lesser amounts of blood. These alternate sites therefore are generally appropriate for use only for test systems requiring relatively small amounts of fluid, or if steps are taken to facilitate the expression of the bodily fluid from the incision site.
The acquisition of the produced bodily fluid, hereafter referred to as the “sampling” of the fluid, can take various forms. Once the fluid specimen comes to the skin surface at the incision, a sampling device is placed into contact with the fluid. Such devices may include, for example, systems in which a tube or test strip is either located adjacent the incision site prior to forming the incision, or is moved to the incision site shortly after the incision has been formed. A sampling tube may acquire the fluid by suction or by capillary action for transport to a testing location.
The bodily fluid sample may be analyzed for a variety of properties or components, as is well known in the art. For example, such analysis may be directed to hematocrit, blood glucose, coagulation, lead, iron, etc. Testing systems include optical (e.g., reflectance, absorption, fluorescence, Raman, etc.), electrochemical, or magnetic means for analyzing the sampled fluid. Typically, a test system takes advantage of a reaction between the bodily fluid to be tested and a reagent present in the test system. For example, an optical test strip will generally rely upon a color change, i.e., a change in the wavelength absorbed or reflected by dye formed by the reagent system used.
A common medical test is the measurement of blood glucose level. The glucose level can be determined directly by analysis of the blood, or indirectly by analysis of other fluids such as interstitial fluid. Diabetics are generally instructed to measure their blood glucose level several times a day, depending on the nature and severity of their diabetes. Based upon the observed pattern in the measured glucose levels, the patient and physician determine the appropriate level of insulin to be administered, also taking into account such issues as diet, exercise and other factors.
In testing for the presence of an analyte such as glucose in a bodily fluid, test systems are commonly used which take advantage of an oxidation/reduction reaction which occurs using an oxidase/peroxidase detection chemistry. The test reagent is exposed to a sample of the bodily fluid for a suitable period of time, and there is a color change if the analyte (glucose) is present. Typically, the intensity of this change is proportional to the concentration of analyte in the sample. The color of the reagent is then compared to a known standard which enables one to determine the amount of analyte present in the sample. This determination can be made, for example, by a visual check or by an instrument, such as a reflectance spectrophotometer at a selected wavelength, or a blood glucose meter. Electrochemical and other systems are also well known for testing bodily fluids for properties on constituents.
Performing the above-discussed steps can be difficult for patients, especially for patients with limited hand dexterity. In a typical procedure, the patient first creates an incision in the skin with a lancet. When the incision is being made, the skin can tend to deform or bulge such that the lancet forms an incision with a greater depth than needed. As one should appreciate, the greater penetration depth of the lancet into the skin results in more pain associated with lancing for the user. Once a sufficient amount of fluid collects as a droplet on the skin, the patient positions a capillary tube over the incision cite and transfers the fluid from the incision onto a test strip with the capillary tube. Usually the droplets of fluid are quite small, and patients, especially those with hand motor control problems, may experience great difficulty in positioning the test strip or capillary tube so as to collect a sample from the droplet. Moreover, the incision may be closed when excessive pressure is applied to the skin by the capillary tube, thereby reducing the fluid supply from the incision. As should be appreciated, patients can become frustrated by this procedure, and consequently, they may perform the test less often or may even quit testing altogether.
Another difficulty with testing is realizing at least a minimum droplet size to ensure a correct test. With devices utilizing capillary transport of the droplet to a test location, sufficient quantity of the droplet is required to be introduced into the capillary passage to sustain its movement to the testing location. The farther the location is from the incision site, the greater quantity of fluid is required. There exists in the art a need to reduce the size of the droplet in such a device so as to minimize patient discomfort but retain sufficient quantity at the test location for an accurate and reproducible result.